Field of the Invention
The present invention relates to a surge protection device for multi-protection mode communications, wherein a plurality of surge protection circuits are provided such that, even though some of the circuits are stopped operating due to damage and any other reasons, the device can operate by another one of the surge protection circuits so as to prevent communications inability states in advance.
Background Art
In general, the development of communications/control systems has been increasing owing to the development of industrial automation and high-speed communications technologies. Such a communications/control system includes a very large scale integrated circuits VLSI owing to the development of semiconductor technologies and thus resistance with respect to a surge becomes weakened, increasing damage day by day. As countermeasures therefor, surge protection devices for power supply and surge protection devices for communications have been suggested to be installed. The surge protection device for power supply can be detached from a power supply system when an obstacle is generated in the power supply system due to the parallel connection of this surge protection device for power supply. However, the surge protection device for communications is connected in serial such that an obstacle very instantly and hugely influences on a communications system at the time of a communications disturbance.
Such a communications surge protection device include passive elements such as a metal oxide varistor MOV, a gas discharge tube GDT, a transient voltage suppressor TVS, a resistor and the like as main elements. The surge protection device loses natural characteristics by a surge generated inside/outside. The surge protection device is inserted in the middle of a line in serial in view of the structure of a communications system. Therefore, it is not possible to carry out normal protection for equipment to be protected when the surge protection device loses the functions thereof. Accordingly, the failure of the surge protection device due to a transient voltage/current can directly cause damage to the equipment. That is, when a surge voltage beyond the protection capacity of an overvoltage protection device is introduced into the device, elements in the overvoltage protection device are likely to be damaged and short-circuited. Particularly, the TVS or the varistor is likely to be the most damaged part and the TVS element has the highest short-circuit ratio.
However, it is not possible to check the failure of the overvoltage protection device with the naked eye. Therefore, the exchange time of the overvoltage protection device is likely to be missed even though the lifespan of the overvoltage protecting device is ended, thereby resulting in the damage to the equipment.
To this end, there has been suggested a technology for detecting a short-circuit of any one or more of the varistors and the TVSs and displaying the detection result by LEDs, thereby enabling immediate countermeasures to be carried out [Patent Document 1]. Further, there has been suggested a technology for operating the life of a varistor and carrying out connection conversion when the life reaches a predetermined critical value [Patent Document 2]. However, the prior art technologies still have a problem that no partial damage instead of such a short-circuit can be recognized, generating damage to equipment when a surge is introduced.
In order to solve the above mentioned problems, there have been suggested technologies for providing a plurality of surge protection circuits and automatically converting one surge protection circuit into any other one if the one surge protection circuit becomes impossible to carry out the surge protection operation [Patent Documents 3 and 4].
As shown in FIG. 1, the prior art surge (overvoltage) protection device includes a plurality of surge discharge parts 300. That is, the plurality of surge discharge parts 300 are provided between an input line discharge part 100 and an output line discharge part 200 so as to be spaced from each other at a predetermined distance, and are selectively connected to the input line discharge part 100 and the output line discharge part 200 so as to prevent a surge or overcurrent, which is introduced from the input line discharge part 100, from being discharged to the output line discharge part 200.
Specifically, the surge discharge part 300 includes a first surge discharge circuit 310 having a first linear resistor 311 and a first TVS 312, which are connected to the input line in serial, and a second surge discharge circuit 320 having a second linear resistor 321 and a second TVS 322, wherein the first surge discharge circuit 310 and the second surge discharge circuit 320 are positioned in parallel. At this time, the first surge discharge circuit 310 and the first surge discharge circuit 320 of the surge discharge part 300 are selectively connected to the input line discharge part 100 by a first connection part 400 and selectively connected to the output line discharge part 200 by a second connection part 500.
At this time, a voltage is applied between the input line discharge part 100 and the output line discharge part 200 so as to check damage to the surge discharge circuit. A checking voltage is applied to an input line 110 through the connection to the input line discharge part 100. Particularly, the checking voltage is applied to the both ends of the input line 110 through the connection to the both ends of the first GDT 120 of the input line discharge part 100.
Further, the voltage between the surge discharge circuits of the surge discharge part 300 connected to the input line discharge part 100 and the output line discharge part 200 is detected to be recognized. That is, if the first surge discharge circuit 310 is connected, the voltage between the first surge discharge circuit 310 and the input and output line discharge parts 100 and 200 can be recognized and, if the second surge discharge circuit 320 is connected, the voltage between the second surge discharge circuit 320 and the input and output line discharge parts 100 and 200 can be recognized. The detected voltage is compared with a reference voltage so as to determine the abnormality of the connected surge discharge circuit. If the abnormality of the connected surge discharge circuit 310 or 320 is determined, the connection is converted from the connected surge discharge circuit 310 or 320 to another surge discharge circuit 310 or 320, which is not damaged.
However, the prior art [Patent Document 3] still has a problem that additional voltages have to be applied in order to determine the damage to the surge discharge circuit.